UAVs and other aircraft typically include a fuel system that includes a fuel bladder for holding fuel. The fuel bladder can be located, for example, within the hollow wings of the UAV. The fuel system also typically includes one or more fuel pickups located within the bladder. The fuel pickup transports the fuel inside the bladder to transfer lines located outside of the bladder. The transfer lines transfer the fuel to downstream components, such as a fuel pump, fuel filter, or sump, and the fuel is ultimately delivered to an engine.
As the engine consumes the fuel contained in the fuel bladder, the air/fuel ratio inside the bladder increases. As the air/fuel ratio reaches high levels (e.g., greater than 1:1), the chances of air or fuel vapor ingestion increases. Vaporized fuel in the system can result, for example, from vaporized fuel present in a closed fuel system. Air can enter the fuel system, for example, due to improper fueling procedures, or leaking fuel line connections or fittings.
When the engine ingests air or fuel vapor, it typically stalls. With conventional fuel pickups, the engine often stalls due to air and/or fuel vapor ingestion prior to consumption of all of the fuel contained in the fuel bladder. As a result, the run time of the engine is unduly shortened.